Shell-and-tube geometry: what is the name of the shortest center-to-center distance between adjacent tubes in a tube bundle?

Introduction / Context:
Tubular geometry in shell-and-tube heat exchangers affects heat transfer area density, pressure drop, mechanical strength, and cleanability. Correct terminology helps communication between process, mechanical, and fabrication teams and prevents costly misunderstandings during design and procurement.

Given Data / Assumptions:

• Regular tube layout on triangular or square pitch.
• Attention on basic spacing parameters: pitch, clearance, ligament.
• Standard drilled tube sheets and straight tubes.

Concept / Approach:
“Tube pitch” is the center-to-center distance between neighboring tubes. It is a primary layout parameter specified along with tube outside diameter (OD). Tube clearance refers to the gap between tube surfaces (pitch − OD). Pitch must be chosen to satisfy mechanical strength, prevent tube-to-tube contact during thermal growth, and allow adequate flow distribution.

Step-by-Step Solution:

Verification / Alternative check:
Design handbooks and TEMA practices list pitch and clearance guidelines and distinguish these terms clearly.

Why Other Options Are Wrong:

• Tube clearance is not center-to-center; it is edge-to-edge spacing.
• “Always less than the tube diameter” is a false absolute; pitch is typically greater than OD.
• “None of these” is incorrect because “tube pitch” is the accepted term.

Common Pitfalls:
Confusing pitch with ligament; choosing an overly tight pitch that complicates rolling/welding and increases risk of vibration or fouling.

Final Answer:
Tube pitch